Multi-touch integrity sensing for capacitive touch screen

ABSTRACT

A method for multi-touch integrity sensing for a multi-touch capacitive touch screen is disclosed. By determining the integrity of touches, a distinction is identified between wanted touches, such as via a finger or stylus, and unwanted touches such as via foreign matter, errors, and the like.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.15/177,489 filed Jun. 9, 2016, the disclosure of which is incorporatedby reference.

FIELD OF THE INVENTION

The present disclosure generally relates to capacitive touchscreenpanels and, more particularly, to a system and method for integritysensing for use in a capacitive touchscreen panel.

BACKGROUND

Touchscreen panels are typically incorporated in various electronicdevices to detect a user input (i.e., user touch or hover) and todisplay content. The touchscreen panels include an active portioncapable of detecting the user input and displaying content. This activeportion is typically formed from a display panel on top of which acapacitive sensing panel is provided which includes multiple layers ofcapacitive sensing circuitry arranged in a pattern.

A capacitive sensing panel may be provided in a touchscreen panel for anelectronic device such as a smart phone, GPS device, tablet computer,mobile media player, remote control device, or any other device capableof using a touchscreen panel. The sensing panel includes a patternedarray of conductive features arranged in an overlapping configuration.For instance, the patterned array of conductive features may includesets of overlapping lines, conductive pads, interleaved structures,diamond structures, lattice structures, and the like. The overlappingconductive features may form capacitive nodes at various points ofoverlap and/or the conductive features may form capacitive nodes betweeneach of the features and a circuit ground. The capacitive sensing panelmay evaluate changes in capacitance at each capacitive node to detect auser touch or hover, such as by a finger or other body part as well asby a tool such as a stylus.

SUMMARY

A method of touch island integrity checking includes identifying a firstset of touched nodes of a capacitive sensing panel by a first mode ofoperation and identifying a second set of touched nodes of thecapacitive sensing panel by a second mode of operation. The methodincludes creating a processing mask based on the second set of touchednodes, and classifying all nodes of the first set of touched nodes inresponse to the processing mask. The method further includes indicatinga processing status including one of a success state and a failure statein response to the classifying.

A further method of touch island integrity checking includes identifyingmutual capacitance touched nodes of a capacitive sensing panel by amutual capacitance mode, identifying self-capacitance touched nodes ofthe capacitive sensing panel by a self-capacitance mode, and creating anode mapping overlay based on self-capacitance touched nodes. The methodalso includes mapping mutual capacitance touched nodes into touchislands according to the node mapping overlay and confirming a touchisland integrity in response to the mapping.

A touch screen controller is disclosed. The controller includes a nodeidentification engine configured to identify a first set of touchednodes of a capacitive sensing panel by a first mode of operation and toidentify a second set of touched nodes of the capacitive sensing panelby a second mode of operation. The controller also has a mask generationengine configured to create a processing mask based on the second set oftouched nodes and a node classification engine configured to classifythe nodes of the first set of touched nodes in response to theprocessing mask. The controller further includes a classified nodeprocessing engine configured to indicate a processing status includingone of a success state and a failure state in response to theclassifying.

In an embodiment, a method comprises: identifying mutual touch islands,wherein each mutual touch island contains certain mutual capacitancenodes of a capacitive sensing panel; identifying self-capacitancetouched nodes of the capacitive sensing panel along a first axis of thecapacitive sensing panel; identifying self-capacitance touched nodes ofthe capacitive sensing panel along a second axis of the capacitivesensing panel; and confirming integrity of the mutual touch islands if:a) a maximum number of the identified self-capacitance touched nodesalong the first or second axes is less than or equal to a count of theidentified mutual touch islands; and b) the count of the identifiedmutual touch islands is less than or equal to a peak area, wherein thepeak area is equal to the number of the identified self-capacitancetouched nodes along the first axis multiplied by the number of theidentified self-capacitance touched nodes along the second axis.

BRIEF DESCRIPTION OF DRAWINGS

The foregoing and other features and advantages of the presentdisclosure will become further apparent from the following detaileddescription of the embodiments, read in conjunction with theaccompanying drawings. The detailed description and drawings are merelyillustrative of the disclosure, rather than limiting the scope of theinvention as defined by the appended claims and equivalents thereof.

Embodiments are illustrated by way of example in the accompanyingfigures not necessarily drawn to scale, in which like numbers indicatesimilar parts, and in which:

FIG. 1A illustrates an electronic device having a multi-touch capacitivetouch screen configured to receive user input, in accordance withvarious embodiments;

FIG. 1B illustrates a logical structure of a touch screen controller, inaccordance with various embodiments;

FIG. 2 illustrates a capacitive sensing panel of the multi-touchcapacitive touch screen, in accordance with various embodiments;

FIG. 3 illustrates a method for multi-touch integrity sensing for themulti-touch capacitive touch screen, in accordance with variousembodiments;

FIG. 4A illustrates a method for multi-touch integrity sensing includingtouch island integrity checking, in accordance with various embodiments;and

FIG. 4B illustrates a method for touch island integrity checking andmulti-touch sensing with self-capacitance nodes, in accordance withvarious embodiments;

FIG. 4C illustrates a method of multi-touch sensing withself-capacitance nodes, in accordance with various embodiments; and

FIGS. 5-6 depict touch scenarios involving multiple touch islands.

DETAILED DESCRIPTION OF THE DRAWINGS

With reference to FIG. 1A, an electronic device 2 comprises any deviceconfigured to receive user input. For example, an electronic device 2may comprise a smart phone, a GPS device, a tablet computer, a mobilemedia player, a remote control device, or any other device as desired.The electronic device 2 further comprises a touch sensitive interfacesystem 10. A touch sensitive interface system 10 is configured to acceptuser input via touching such as from the user's body and/or a tool suchas a stylus. The touch sensitive interface system 10 also providesoutput, such as by a human-readable display.

More specifically, the touch sensitive interface system 10 comprises amulti-touch capacitive touch screen 14, a touch screen controller 12,and a system on a chip 16. The system on a chip 16 may comprise aprocesser, interface, circuitry, and/or the like configured to directthe flow of input and output data to a multi-touch capacitive touchscreen 14 and an associated touch screen controller 12. A touch screencontroller 12 is configured to be in logical communication with thesystem on a chip 16. The touch screen controller 12 comprises aprocessor and a memory in logical communication with the multi-touchcapacitive touch screen 14. The touch screen controller 12 may performvarious methods with respect to the multi-touch capacitive touch screen14 as discussed further herein.

With reference to FIG. 2, a multi-touch capacitive touch screen 14includes a capacitive sensing panel 20. The capacitive sensing panel 20includes a drive array 26 and a sense array 28 operable by a touchscreen controller 12 in a mutual capacitance mode and a self-capacitancemode. A drive array 26 comprises an array of conductive featuresarranged in a matrix with respect to the sense array 28. Similarly, thesense array 28 comprises an array of conductive features arranged in amatrix with respect to the drive array 26. For example, the drive array26 comprises a first drive line 27-1, a second drive line 27-2, a thirddrive line 27-3, and any number n of drive lines, such as including ann^(th) drive line 27-n. In like manner, the sense array 28 comprises afirst sense line 29-1, a second sense line 29-2, a third sense line29-3, and any number m of sense lines, such as including an m^(th) senseline 29-m. In various embodiments, an equal number of sense lines 29 anddrive lines 27 exist, whereas in further embodiments, the number ofsense lines 29 and drive lines 27 differ. Moreover, the touch screencontroller 12 may repurpose various sense lines 29 to function as drivelines 27, and various drive lines 27 to function as sense lines 29, fromtime to time. For example, during a self-capacitance mode discussedbelow, one or more drive lines 27 or sense lines 29 may perform bothdrive and sense functions, for instance, a drive line 27 may also serveas a sense line 29 so that self-capacitance (rather than mutualcapacitance) is monitored.

The drive array 26 and the sense array 28 may overlap. While FIG. 2depicts the drive lines 27 of the drive array 26 overlapping the senselines 29 of the sense array 28 orthogonally, one may appreciate thatother shapes than lines may be implemented, and the shapes may overlapother than orthogonally, for instance, such as being interleaved, or atvarious angles, or otherwise, as desired.

The drive array 26 is connected to drive circuitry 24. The drivecircuitry 24 excites one or more drive lines of the drive array 26 suchas with an electrical waveform. The sense array 28 is connected to sensecircuitry 22. The sense circuitry 22 detects voltage and/or currentperturbations on one or more sense lines of the sense array 28 that maybe induced in response to the electrical waveform on the drive array 26and/or further in response to external influences such as the presenceof a finger, stylus, or unwanted material such as water. In variousembodiments, these perturbations arise from capacitive interactionbetween the drive array 26, the sense array 28, and/or proximate objectssuch as a finger or stylus that is interacting with the multi-touchcapacitive touch screen 14. As such, one may say that the drive array 26and sense array 28 share “nodes,” wherein a node 13 arises at eachintersection of a sense line 29 or drive line 27 with a drive line 27 orsense line 29, respectively. In various embodiments, such an arrangementfacilitates operation in a mutual capacitance mode discussed below.

Furthermore, the drive array 26 and sense array 28 may operateindependently so that a single node 13 arises between a drive line 27and/or sense line 29 and a circuit ground, rather than nodes 13corresponding to intersections of drive lines 27 of the drive array 26and sense lines 29 of the sense array 28. For instance, the drive array26 is connected to drive circuitry 24 and has one or more drive lines 27excited by the drive circuitry 24 with an electrical waveform. The drivearray 26 may also serve as a sense array 28, thus having a dual purpose.Induced voltage and/or current perturbations may arise on a drive line27 as a result of the presence of a finger, stylus, or unwanted materialsuch as water, parasitically sinking current from the drive line 27 to aground. Thus, each drive line 27 of the drive array 26 may be consideredto be a single node 13, as may each sense line 29 of the sense array 28.Stated another way, each line may be conceptualized as having multiplenodes, as is the case when the mutual capacitance mode is implemented,but every node of the line may be considered equipotential with everyother node of the line, so that the line is effectively a single node.While the drive array 26 and sense array 28 are depicted as separatearrays of orthogonal lines in FIG. 2, one may appreciate that the drivearray 26 may be its own sense array 28, and vis-a-versa. In variousembodiments, such an arrangement facilitates operation in aself-capacitance mode.

As briefly mentioned, a capacitive sensing panel 20 operates in at leasttwo distinct modes, a mutual capacitance mode and a self-capacitancemode.

In a self-capacitance mode, the touch screen controller 12 configuresthe sense circuitry 22 to sense the capacitance between any given columnor row (e.g., a sense line 29 forming a node 13/equipotential nodes 13)and a surrounding panel reference (for example, ground). By sensing achange in self-capacitance for the given column or row, the sensecircuitry 22 detects a user touch or hover at or near that given columnor row. Advantageously, self-capacitance mode sensing provides betterrejection of unwanted foreign matter, such as water, in contact with themulti-touch capacitive touch screen 14. Unfortunately, self-capacitancemode sensing is prone to a ghosting problem associated with amulti-touch situation because the entire length of the given column orrow of the sense line 29 is used to sense (e.g., the entire sense line29 forms a single node 13) and thus the sense circuitry 22 is not ableto unambiguously distinguish between different touch/hover instancesfalling along a same row or column.

In a self-capacitance mode, the touch screen controller 12 directs thedrive circuitry 24 to excite the drive array 26 with a waveform andrepurpose the drive array 26 to serve a dual role also as a sense array28, and/or may repurpose the sense circuitry 22 to further function as adrive circuitry 24, driving the sense array 28 with a waveform. Thetouch screen controller 12 monitors the amount of charge (or current)needed to substantially fully charge a capacitance disposed between oneor more associated nodes 13 of the array and a circuit ground. Thestored charge may discharge via a current directly coupled from the node13 to a finger, stylus or other touch (and to a lesser degree, viafringe field coupling to adjacent nodes 13). A water droplet increasesthe fringe field strength, enhancing the capacitive coupling between thenode 13 and adjacent nodes 13 of adjacent lines. However, because theadjacent nodes 13 of adjacent lines are much smaller current sinks thana finger, stylus or other touch, the effect of a water droplet issubstantially less than that of a desired touch and may be filtered outas an error. Moreover, the effects of a water droplet may be evenfurther diminished by driving the adjacent lines with a waveform similaror identical to that exciting the drive array 26, in this manner,substantially zeroing any potential difference between the node 13 andadjacent nodes 13 of the adjacent lines, and thus substantially zeroingany potential current flow via a fringe field between nodes 13.

In a mutual-capacitance mode, the touch screen controller 12 configuresthe sense circuitry 22 to sense the capacitance at an intersection point(node 13) between one column/row of a sense line 29 and one row/columnof a drive line 27. Thus, each row or column is associated with multiplenodes 13 in a mutual-capacitance mode, whereas each is associated withonly a single node 13 in a self-capacitance mode. By sensing a change inmutual-capacitance at a given node 13 between a sense line 29 and adrive line 27, the sense circuitry 22 detects a user touch or hover ator near that given intersection point. Advantageously,mutual-capacitance mode sensing provides higher resolution for detectingthe particular location of a user touch or hover, and enables the sensecircuitry 22 to distinguish between and identify the locations ofmulti-touch/hover situations, including along the same row or column.Unfortunately, a mutual-capacitance mode is prone to falsely detectingunwanted foreign matter, such as water in contact with the multi-touchcapacitive touch screen 14 as a touch, because the water also changesthe mutual-capacitance at an affected node 13.

During a mutual capacitance mode, the touch screen controller 12evaluates the capacitance existing between the drive array 26 and sensearray 28 at each node 13 while directing the drive circuitry 24 toexcite the drive array 26 with a waveform. The touch screen controller12 directs the sense circuitry 22 to monitor the sense array 28 toquantify a potentially coupled signal coupled to the sense array 28 fromthe drive array 26. For instance, a fringe field may couple the sensearray 28 to the drive array 26 at the location of each node 13. Afinger, stylus, or other touch desired to be detected effectively stealscharge from the node 13 by diverting current that would otherwise passthrough the fringe field between the sense array 28 and drive array 26to a current sink, such as ground. As such, a net reduction in mutualcapacitance at the node 13 occurs. Furthermore, a water dropletincreases the fringe field strength, enhancing the capacitive couplingbetween the sense array 28 and drive array 26 at the node 13 andincreasing the flow of current through the fringe field between thesense array 28 and the drive array 26, introducing anomalies to thesensed waveform detected by the sense circuitry 22. One may appreciatethat a water droplet increases coupling (and current transfer) andincreases capacitance between the sense array 28 and drive array 26 atthe node 13, while a touch steals charge from the node 13 and decreasesthe capacitance. As such, a touch and a water droplet are in someinstances identifiable by their opposite effect on capacitance at eachnode 13. The effect of water may balance, or overpower the effect of atouch, causing detection errors.

While the mutual capacitance mode enables detection of multiplesimultaneous touches along a same row or a same column, theself-capacitance mode enables the differentiation of finger or stylustouches from water droplets at the cost of being less able to resolvemultiple simultaneous touches along a same row or a same column. Theopposite advantages and disadvantages of self-capacitance mode andmutual-capacitance mode often lead the system designer to chooseoperation of the panel in one or the other mode based on whether thepanel is being provided in an environment where water rejection ispreferred or an environment where multi-touch detection (with accuratelocation resolution) is preferred. Furthermore, the system may be chosento change from one mode to another, or to operate in both modes. Thedate generated by each mode may be combined to resolve touches. However,because the two modes are relatively independent, there is a need in theart for solutions which would enable a panel to enjoy the benefits ofboth self-capacitance mode and mutual-capacitance mode while alsoidentifying when the two modes diverge so that the integrity of the dataproduced may be determined to be more or less reliable.

With reference to FIG. 1B and FIG. 3, a touch screen controller 12 maycomprise various logical modules, which, in connection with theelectronic device 2 of FIG. 1B, and the multi-touch capacitive touchscreen 14 of FIGS. 1A and 2, may interoperate to execute variouscomputer implemented methods, such as a method for multi-touch integritysensing for the multi-touch capacitive touch screen 100 (FIG. 3) asdiscussed further herein.

A touch screen controller 12 may comprise a bus 25 and a bus controller23. The bus 25 may comprise a physical bus, or may comprise a logicalbus resident in the touch screen controller 12. Moreover, the buscontroller 23 may comprise a logical unit of the touch screen controller12 configured to direct communication between and among the differentengines and modules connected to the bus 25.

The touch screen controller 12 may comprise a node identification engine40. A node identification engine 40 may comprise an aspect of aprocessor and/or electronic storage memory configured to identify afirst set of touched nodes by a first mode of operation and a second setof touched nodes by a second mode of operation (step 101). For instance,a first mode of operation may be a mutual capacitance mode or aself-capacitances mode. Similarly, a second mode of operation may be aself-capacitance mode or a mutual capacitance mode. In variousembodiments, the first mode of operation and the second mode ofoperation are different modes.

The touch screen controller 12 may also comprise a mask generationengine 36. A mask generation engine 36 may communicate with the nodeidentification engine 40 via the bus 25 under instruction of the buscontroller 23 and may receive data representing a plurality of touchednodes. For instance, the mask generation engine 36 may receive datarepresenting the second set of touched nodes. In response to receivingthe data representing the second set of touched nodes, the maskgeneration engine 36 may perform various calculations to form a union ofthe second set of touched nodes with mask rules to create a processingmask based on the second set of touched nodes. As used herein, aprocessing mask means a data array indicating the state information ofeach node of the capacitive sensing panel 20. State information maycomprise a scalar numerical value representative of the strength of thecapacitance associated with that node in the second mode. Stateinformation may comprise a vector value representative of a change ofcapacitance associated with that node during at least one of the firstmode and the second mode over time. Moreover, state information maycomprise a quality index associated with that node and indicative of alikelihood that that node comprises a touched node (e.g., a node thathas a capacitance associated with a wanted touch such as a stylus touchor a finger touch and not associated with an unwanted touch such ascaused by foreign matter, including water.)

Thus, the second set of touched nodes may comprise self-capacitancetouched nodes which are less susceptible to the corrupting influence offoreign material, but which afford a lesser degree of positionalresolution for touches than do mutual-capacitance touched nodes. Thestate information may be a scalar value representing a self-capacitancestrength for each node. Moreover, the state information may include aself-capacitance touch flag, which is a binary value indicating whetherthe self-capacitance strength exceeds a self-capacitance touchthreshold. The self-capacitance touch threshold may be a predeterminedvalue, and self-capacitance strengths that exceed this threshold may beassociated with a wanted touch such as a finger or stylus touch, whilethose that do not exceed this threshold are not associated with a wantedtouch. In this manner, it may be said that the mask generation engine 36creates a processing mask based on a second set of touched nodes (step105).

The touch screen controller 12 may comprise a node classification engine34. The node classification engine 34 classifies nodes of the first setof touched nodes in response to the processing mask (step 107). The maskgeneration engine 36 passes the processing mask to the nodeclassification engine 34 via the bus 25 at the direction of the buscontroller 23 and the node identification engine 40 passes the first setof touched nodes to the mask generation engine 36 via the same. Aclassified node processing engine 32 may receive the processing mask,which is based on the second set of touched nodes, and may receive datarepresentative of the first set of touched nodes, and may output aclassification of the first set based on the processing mask. One suchclassification is an integrity index. An integrity index may be anumerical value associated with each node of the first set of nodes, themagnitude of which is directly correlated to one or more variable of theprocessing mask.

For example, the state information within the processing mask mayinclude a self-capacitance touch flag. The first set of touched nodesmay comprise mutual capacitance touched nodes and each variable of theset may include a mutual capacitance strength of one such node. Byperforming mathematical computations involving the union of the firstset of touched nodes to the processing mask, an integrity index valuemay be generated for each mutual capacitance touched node showingwhether that node is associated with a valid touch (touch state), isassociated with foreign material such as water (foreign material state)or is associated with a detection error (null state).

For example, the node classification engine 34 returns a touch state ifboth the mutual capacitance strength and the self-capacitance touch flagfor a node indicate a valid touch. For instance, if the self-capacitancetouch flag indicates a touch, and the mutual capacitance strengthexceeds a first mutual capacitance strength threshold, a valid touch maybe indicated. The node classification engine 34 may return a foreignmaterial state if the self-capacitance touch flag fails to indicate avalid touch, while the mutual capacitance strength fails to indicate asimilar valid touch. The node classification engine 34 may return a nullstate if the self-capacitance touch flag and the mutual capacitancestrength indicate contradictory statuses.

Finally, the node classification engine 34 may pass the integrity indexvalue of the classified nodes to the classified node processing engine32 via the bus 25 under the direction of the bus controller 23. Theclassified node processing engine 32 may process classified nodes of thefirst set (step 109). More specifically, the classified node processingengine 32 may evaluate the integrity index value of the classified nodesagainst integrity rules. In the event that the processing succeeds(integrity rules are met), the classified node processing engine 32transmits processed results to the output module 30 for distribution tofurther systems and methods (“Processing Succeeds”). The output module30 provides output to further systems and methods at the direction ofthe bus controller 23 and via the bus 25 (step 111).

In response to the processing failing (integrity rules are not met), thenode classification engine 34 directs the mode selection engine 38 toswitch the touch screen controller 12 to a second mode of operation(step 115), so that touch sensing may continue by a different mechanism.In the second mode of operation, aspects of the touch screen controller12 such as the classified node processing engine 32 process the firstset or the second set of touched nodes by a second mode of operation(step 117). A second mode of operation may include evaluating differentnodes in different ways, for instance, evaluating the second set oftouched nodes (self-capacitance touched nodes) in view of differentintegrity rules than were applied in the failed evaluation of the firstset of touched nodes (mutual capacitance touched nodes). The second modeof operation proceeds and concludes again with the output module 30providing output to further systems and methods at the direction of thebus controller 23 and via the bus 25 (step 111).

With reference to FIGS. 1B, 3, 4A, and 5, a method for multi-touchintegrity sensing for the multi-touch capacitive touch screen 100 may befurther refined as illustrated in FIG. 4A. For instance, a method formulti-touch integrity sensing including touch island integrity checking200 may include various refinements of various steps of the method formulti-touch integrity sensing for the multi-touch capacitive touchscreen 100. For example, the method for multi-touch integrity sensingincluding touch island integrity checking 200 may comprise identifyingmutual capacitance touched nodes and creating a first touch island 52-1and a second touch island 52-2 of these nodes by a mutual capacitancemode of operation (step 201 of step 101). Throughout this disclosure, atouched node is a node 13 (FIG. 2) associated with a charge indicativeof a touch. Each the touched nodes of the mutual capacitance mode formsone or more touch island. A touch island is a grouping of nodes witheach node adjacent to at least one other node of an adjacent row/column,both having a mutual capacitance strength with an value greater than afirst mutual capacitance strength detection threshold.

Subsequently, self-capacitance touched nodes along a first axis 42 andsecond axis 44 may be identified in a self-capacitance mode of operation(step 203 of step 101). The identified self-capacitance touched nodesmay be processed to create a node mapping overlay 46 (step 205 of step107). The node mapping overlay 46 based on the identifiedself-capacitance touched nodes is a specific instance of a processingmask based on a second set of touched nodes. The node mapping overlay 46comprises a matrix of values that depict areas of a valid touch (activeregion 61) and that depict areas lacking a valid touch (inactive region62) with distinctive indications, such as a binary indication, or amatrix of scalar values that will indicate the presence or absence of avalid touch once compared to a threshold. The valid touches that areidentified in the self-capacitance mode are identified by determiningthe intersection of a row node associated with a self-capacitancestrength maxima such as TX_Peak 50 with a column node associated with aself-capacitance strength maxima such as RX_Peak 48. Subsequently, themutual capacitance touched nodes are mapped into the active region 61and the inactive region 62 by overlaying the node mapping overlay 46. Asone may appreciate by viewing FIG. 5, the first touch island 52-1 isconfirmed as a valid touch island because it is within the active region61, while the second touch island 52-2 is ignored as an invalid touchisland because it is within the inactive region 62 (step 207 of step107). As a further verification, the integrity of the valid touchisland(s), which in this instance is only first touch island 52-1, isconfirmed (step 209 of step 109). As mentioned previously, the integritywill be confirmed by evaluating an integrity index value of theclassified nodes (in this instance, the first touch island 52-1) againstintegrity rules.

FIGS. 4B, 4C depict a first method of confirming the integrity (step209). With reference now to FIGS. 1B, 3, 4A-C, and 5, a first method ofconfirming the integrity comprises a method for touch island integritychecking and multi-touch sensing with self-capacitance nodes 209. Asused with reference to method 209, “integrity” means that the number ofidentified touch islands is consistent with various integrity rules. Inother words, the data available to the classified node processing engine32 does not contain internal inconsistencies which would suggest error.The method 209 includes five sub-steps to effectuate the comparison ofthe integrity index against integrity rules in order to confirm theintegrity of the touch islands. For example, a first integer count ofthe number of first axis 42 self-capacitance maxima 50 (“TX_Peak”) amongthe self-capacitance touched nodes is summed (step 2091)(“TX_Peak_Count”). A second integer count of the number of second axis44 self-capacitance maxima 48 (“RX_Peak”) among the self-capacitancetouched nodes is summed (step 2093) (“RX_Peak_Count”). Finally, a thirdinteger count of the number of valid touch islands, which in thisinstance has been previously determined to be one touch island, thefirst touch island 52-1 is summed (step 2095)(“Valid_Mutual_Island_Count”). A peak area (“Peak Area”) is computedcomprising the product of TX_Peak_Count multiplied by RX_Peak_Count(step 2097).

Having derived these values, a touch island integrity check truthstatement is executed. Specifically, this integrity check comprisesevaluating the truth or falsity of the following statement (step 2099):

Max(TX_Peak_Count, RX_Peak_Count)<=Valid_Mutual_Island_Count<=Peak Area

For FIG. 5, the statement would be:

MAX(1,1)<=1<=1*1 which would be TRUE, however, if second touch island52-2 had not been excluded for lying outside of the active region of thenode mapping overlay 46, the statement would have returned FALSE and itwould be apparent that the integrity of the data developed in thepreceding steps of method 300 was lacking. By concluding with anintegrity check 209 false indications of touch may be diminished.

As briefly mentioned, if the check returns TRUE, the integrity of thetouch islands are confirmed (step 2092 of step 111). If the checkreturns FALSE, the integrity of the touch islands are not confirmed, andso the second set of touched nodes is processed by a second mode ofoperation, specifically, multi-touch sensing is performed withself-capacitance nodes of first axis 42 and second axis 44, rather thanmutual capacitance nodes (step 2094 of step 115). This transition to asecond mode of operation is done because the data available to theclassified node processing engine 32 contains internal inconsistencieswhich would suggest that some of the data collected in the mutualcapacitance mode is erroneous. The presence of this erroneous data maylead to incorrect detection of or failure to detect a touch, orinaccurate or imprecise resolution of the placement of the touch.

The specific implementation of step 2094 will be elaborated withparticular reference to FIG. 4C. The touch screen controller 12 sums allmutual capacitance strengths for all nodes that are within a touchisland 52-1, 52-2 (“Sum_Section”) (step 2096). In response to theSum_Section not exceeding a first sum strength threshold (“Valid_Str”),the integrity of the touch island fails and an error state is returnedindicating that multi-touch sensing cannot be performed in bothmutual-capacitance and self-capacitance modes (step 2103).Alternatively, in response to the Sum_Section exceeding Valid_Str (step2098), there exists sufficient data from the mutual-capacitance mode tosuggest a touch, though the data may contain corruption, so that it isnot as accurate or precise as desired. Thus, touch island 52-1 or 52-2is validated and the integrity of the touch island confirmed, but thecount remains unknown. However, TX_Peak_Count and RX_Peak_Count havebeen determined from self-capacitance mode, so that by again applyingthe rule Max(TX_Peak_Count,RX_Peak_Count)<=Valid_Mutual_Island_Count<=Peak Area, whereValid_Mutual_Island_Count is this time an unknown, a range of potentialvalues of Valid_Mutual_Island_Count is derived. In this instance, theValid_Mutual_Island_Count is returned as a range, rather than a count oftouch islands, because of the limited confirmatory information availableduring self-capacitance mode, particularly when multiple touchescoincide along the same row or column. The Valid_Mutual_Island_Count isreturned as a range (step 2105) which for FIG. 5 would be1<=Valid_Mutual_Island_Count<=1. Thus, one may appreciate that the rangemay in some instances be so small as to be determinative.

With additional reference to FIG. 6, in other scenarios, the range isnot determinative. For instance, FIG. 6 depicts three RX_Peaks 48-1,48-2, 48-3 and two TX_Peaks 50-1, 50-2. There exist five touch islands52-1, 52-2, 52-3, 52-4, and 52-5. When the specific implementation ofstep 2094 is applied, the rule Max(TX_Peak_Count,RX_Peak_Count)<=Valid_Mutual_Island_Count<=Peak Area works out toMAX(2,3)<=Valid_Mutual_Island_Count<=2*3. Thus theValid_Mutual_Island_Count is known to be between 3 and 6, though theactual count of touch islands is five, as shown in FIG. 6.

An advantage of the disclosed implementation is that the design supportsmultiple finger touch detection (using the mutual capacitance sensingmode) and water droplet rejection (using the self-capacitance sensingmode). Thus, the design enables provision of very fine multi-touchaccuracy and linearity owing to the mutual capacitance sensing operationas well as operation in hostile and mobile environments. Whilesequential operation of mutual capacitance sensing and self-capacitancesensing modes is discussed for brevity, one may appreciate that aplurality of sense arrays and/or drive arrays may be so arranged as topermit simultaneous operation of a touch screen in both modes.

The foregoing description has provided by way of exemplary andnon-limiting examples a full and informative description of one or moreexemplary embodiments of this invention. However, various modificationsand adaptations may become apparent to those skilled in the relevantarts in view of the foregoing description, when read in conjunction withthe accompanying drawings and the appended claims. However, all such andsimilar modifications of the teachings of this invention will still fallwithin the scope of this invention as defined in the appended claims.

What is claimed is:
 1. A method, comprising: identifying mutual touchislands, wherein each mutual touch island contains certain mutualcapacitance nodes of a capacitive sensing panel; identifyingself-capacitance touched nodes of the capacitive sensing panel along afirst axis of the capacitive sensing panel; identifying self-capacitancetouched nodes of the capacitive sensing panel along a second axis of thecapacitive sensing panel; and confirming integrity of the mutual touchislands if: a) a maximum number of the identified self-capacitancetouched nodes along the first or second axes is less than or equal to acount of the identified mutual touch islands; and b) the count of theidentified mutual touch islands is less than or equal to a peak area,wherein the peak area is equal to the number of the identifiedself-capacitance touched nodes along the first axis multiplied by thenumber of the identified self-capacitance touched nodes along the secondaxis.
 2. The method of claim 1, further comprising, if integrity of themutual touch islands is not confirmed, then: for each mutual touchisland, summing mutual capacitance strength values for said certainmutual capacitance nodes included in the mutual touch island;determining if the sum of the mutual capacitance strength values exceedsa threshold; if yes, confirming integrity of that mutual touch island.3. The method of claim 2, further comprising identifying a range for anumber of detected mutual touch islands that is greater than or equal tothe maximum number of the identified self-capacitance touched nodesalong the first or second axes but less than or equal to the peak area.4. A method, comprising: identifying touch islands detected using amutual capacitance sensing operation; identifying first touch nodesdetected using a self-capacitance sensing operation along a firstsensing axis; identifying second touch nodes detected using theself-capacitance sensing operation along a second sensing axis; andconfirming integrity of the identified touch islands if: a) a count ofthe identified mutual touch islands is greater than or equal to amaximum of the number of identified first or second touch nodes; and b)the count of the identified mutual touch islands is less than or equalto a peak area, wherein the peak area is equal to the product of thenumber of first touch nodes and second touch nodes.
 5. The method ofclaim 4, further comprising, if integrity of the touch islands is notconfirmed, the confirming the integrity of each touch island if strengthof the touch island exceeds a threshold.
 6. The method of claim 5,further comprising identifying a range for a number of detected touchislands that is greater than or equal to maximum of the number ofidentified first or second touch nodes but less than or equal to thepeak area.